四川盆地龙王庙组优质储层形成与分布的主控因素

Controlling factors of formation and distribution of Lower Cambrian Longwangmiao Formation high-quality reservoirs in Sichuan Basin,China

下寒武统龙王庙组是四川盆地安岳特大型气田的主力储层。本文基于盆地周缘露头、钻井岩心和薄片资料，通过龙王庙组地层对比、储层岩石学、物性特征、成岩作用等的研究，探讨了龙王庙组储层形成分布的控制因素。四川盆地龙王庙组整体上具有可对比性，储层岩性主要为粉－细晶（残余）砂屑白云岩、粉－细晶（残余）鲕粒白云岩、粉－细晶白云岩。储层属于中低孔低渗型。孔隙度＞2％的储层厚度多在20-60 m，川中磨溪地区较高石梯地区厚，向西北方向剥蚀，向东南方向厚度减小。龙王庙组储层形成和分布主要受控于3个因素：拉张槽继承性古地貌、同生期喀斯特作用和液态烃充注作用。拉张槽断层下盘形成的古地貌高地控制了龙王庙组颗粒滩的发育；同生期大气淡水溶蚀作用形成粒间溶孔和粒内溶孔，为后期成岩流体的进入和溶蚀孔洞的扩溶奠定了基础；生排烃高峰期的烃类充注作用，既能形成大量孔隙，又能对储层起到积极的保持作用。绵阳—长宁拉张槽东西两侧断阶形成的古地貌高地控制了龙王庙组早期优质储层的形成和分布；中三叠世期间拉张槽内下寒武统供烃中心与川中古隆起重叠地区是龙王庙组晚期优质储层最发育地区。四川盆地内龙王庙组优质储层最发育和天然气大规模成藏最有利地区均是绵阳－长宁拉张槽与川中古隆起相重叠区的东侧，即高石梯—磨溪地区。

The Lower Cambrian Longwangmiao Formation is the play of the Anyue supergiant gas field in Sichuan Basin.Based on the integrated study of the outcrops on the basin margin and the drilling cores in Sichuan Basin,this paper discusses the controlling factors of the formation and distribution of the high-quality reservoirs of the Longwangmiao Formation through the researches on the strata correlation,reservoir petrology,property characteristics and diagenesis etc..The Longwangmiao Formation could be well correlated in the basin scale,and the reservoir rocks are composed of dolarenite dolomite,oolitic dolomite and crystalline dolomite.The reservoir is of the pore-fracture type with low porosity and low permeability.The reservoir thickness with the porosity over 2% is about 20-60 m.The reservoir in the Moxi area is much thicker than that in the Gaoshiti area.The penecontemporaneous selective fresh water dissolution and liquid hydrocarbon filling have been controlled by the Early Cambrian Mianyang-Changning intracratonic sag to a certain extent.Three factors control the formation and distribution of the good-quality reservoir rocks in Longwangmiao Formation,that is,the inherited palaeogeomorphology of the intracratonic sag,the contemporaneous karst and the liquid hydrocarbon filling.The paleohigh formed by the footwall of margin fault of the intracratonic sag controls the distribution of the grain bank of Longwangmiao Formation. The intergranular and intragranular dissolution pores produced by the contemporaneous atmospheric freshwater karstification are important for the upcoming fluid filling and further dissolution.The hydrocarbon filling at the peak period of the generation and expulsion of the source rocks is beneficial to the increase of pores and the protection of the previous pores.The paleohigh formed by the faults along the two sides of the Mianyang-Changning intracratonic sag controls the formation and distribution of the early high-quality reservoirs,and the overlapping areas of the Lower Cambrian hydrocarbon-generating center and the Chuanzhong paleouplift are the most favorable areas of the late good-quality reservoirs.The most profitable areas for the distribution of the high-quality reservoir rocks and natural gas accumulations in Longwangmiao Formation are the eastern part of the overlapping areas of the Mianyang-Changning intracratonic sag and the Chuanzhong paleouplift,that is,the Gaoshiti-Moxi area.